Titanium alloys are more and more widely used in the aviation manufacturing industry due to their high strength, good mechanical properties and strong corrosion resistance. With the increasing proportion of titanium alloys in aircraft, the numerical control of titanium alloy aviation structural parts The impact of processing efficiency on aviation manufacturing enterprises is also increasing.
Titanium alloy is a difficult-to-machine material, its relative machinability is 0.15 to 0.25, and the processing efficiency is only 10% of that of aluminum alloy. Therefore, the low processing efficiency of titanium alloy aviation structural parts seriously restricts the mass production of modern aircraft. Achieving efficient vowin.cn/en/News/news1251.html' target='_blank'>machining of titanium alloy aerospace structural parts has become a topic of common concern for aerospace manufacturers, CNC equipment manufacturers and tool manufacturers.
01 Machining performance of titanium alloy
Titanium alloy has the characteristics of good mechanical properties, strong corrosion resistance and small specific gravity. However, in machining, the machining performance of titanium alloys is very poor, mainly in the following aspects:
(1) Powerful cutting force.
Titanium alloy material has high strength, and the cutting resistance generated during cutting is powerful, resulting in a large amount of cutting heat generated by the cutting edge;
(2) Low thermal conductivity.
Titanium alloy has low thermal diffusivity, and a large amount of cutting heat is concentrated in the cutting area;
(3) The tool tip stress is large.
The plasticity of titanium alloy is low, and the chips generated by processing are extremely easy to bend, resulting in a short contact length between the chip and the rake face, so the force per unit area on the cutting edge increases, resulting in stress concentration at the tip of the tool;
(4) The friction force is large.
The elastic modulus of titanium alloy is small, resulting in increased friction between the front and flank surfaces;
(5) High chemical activity.
At high cutting temperature, titanium element is easy to chemically react with hydrogen, oxygen, nitrogen and other gases in the air to form a hard surface layer and accelerate tool wear.
02 Titanium alloy efficient processing equipment
In order to meet the efficient processing of titanium alloy structural parts, the new titanium alloy processing equipment presents the following development trends:
(1) High torque.
Titanium alloy has high strength, and the cutting force is very large during processing. An obvious feature of titanium alloy processing machine tools is that the spindle torque and swing angle torque are large.
(2) Application of electric spindle.
High-power, high-torque electric spindles have been used in titanium alloy processing.
(3) Horizontal machining centers are used in titanium alloy machining.
The horizontal machining center is convenient for chip removal, which is beneficial to improve the processing efficiency and processing quality.
(4) High pressure internal cooling.
In titanium alloy machining, the cutting heat is concentrated on the tip of the tool, which is easy to cause tool wear or damage. The high-pressure internal cooling can accurately spray the cutting area to take away the cutting heat.
03 Titanium Alloy High Efficiency Machining Tool
The machinability of titanium alloys is poor, and the cutting speed of traditional machining methods generally does not exceed 60m/min.
The rough machining of titanium alloy is mainly to obtain the maximum metal removal rate by means of large depth of cut, low speed and low feed; for finishing, PVD-coated carbide tools are used for high-speed milling with small width of cut and large depth of cut to obtain high-efficiency cutting. .
Therefore, titanium alloy machining tools are mainly improved on how to avoid chattering, reduce cutting force and reduce cutting temperature during strong cutting.
04 Titanium Alloy High Efficiency Machining Tool
(1) Titanium alloy face milling:
When face CNC milling titanium alloy parts, the milling method with small depth of cut and high feed is used to obtain efficient machining. The principle of high-feed milling is to reduce the main declination angle of the tool, so that the tool can still maintain a small chip thickness under high feed, so as to reduce the cutting force at high feed and achieve low cutting speed. Get high feed rates and increase the metal removal rate per depth of cut.
At the same time, the cutting force is vertically upward, the tangential force is small, and the power consumption is also small. This processing method does not require high power and rigidity of the machine tool, and is widely used.
(2) Titanium alloy groove processing:
Slot cavity is a main feature of titanium alloy aerospace structural parts, with high material removal rate and large workload, so slot cavity machining is the key to efficient machining of titanium alloy parts (see Figure 1). Powerful cutting with large depth of cut, low speed, and low feed for maximum metal removal is an effective method for roughing titanium alloys. At present, the powerful milling tool for roughing titanium alloy is widely used with the highest efficiency of corn milling cutter.
(3) Fillet processing technology:
In order to reduce the weight of the aircraft, the rounded corners of the cavity corners of the aircraft structural parts are usually small and need to be machined with a milling cutter with a smaller diameter. Due to the sudden change of the cutting amount at the fillet, the cutting force varies greatly. In the case of sudden changes in cutting force, the tool easily vibrates, and even chipping occurs, resulting in serious tool wear and low processing efficiency.
Plunge milling is the best way to solve corner machining efficiency. Plunge milling has less vibration than conventional milling, and the cutting method is more efficient in removing corner allowance. By plunging the corners with plunging cutters of different diameters, most of the corner allowance can be removed, and then using the end mill to remove the residues produced by the plunging milling can greatly improve the processing efficiency.
(4) Precision side milling technology:
When finishing the side wall, the discontinuity of milling is used to achieve the purpose of high-speed cutting, so as to improve the surface quality and processing efficiency of the parts. When finishing the flank, due to the small cutting width, the cutting time per revolution of the cutter teeth is very short, that is, the cooling time is very long.
In the case of sufficient cooling, the cutting temperature can be effectively controlled, so the cutting speed can be greatly increased to improve the processing efficiency, as shown in Figure 2 and Figure 3. High-speed cutting and finishing of titanium alloys with PVD-coated solid carbide milling cutters or super-dense-pitch carbide milling cutters can greatly improve machining efficiency and machining accuracy.
(5) Simulation optimization technology: The cutting allowance of titanium alloy structural parts will change continuously during rough machining.
The NC programs compiled by the current CAM software can often only set fixed cutting parameters. In order to avoid the impact on the tool and the machine tool caused by the excessive cutting amount of the local program, the usual method is to reduce the overall cutting parameters to ensure the tool life and part quality. , so the processing efficiency is extremely low.
Vericut’s simulation optimization technology can solve this problem very well. The cutting parameter optimization library is set up by Vericut software, and the software is used for simulation. The actual machining allowance and cutting conditions are guessed through the simulation, and the cutting parameters in the program are optimized according to the machining allowance and cutting conditions. It not only prolongs the tool life, ensures the quality of the parts, but also improves the processing efficiency.